MEANS FOR ANCHORING A ROCK BOLT MADE OF CONCRETE STEEL IN A DRILL HOLE

Abstract: An anchoring means for anchoring a rock bolt made of concrete steel in a drill hole. The anchoring means comprises a body portion (1) intended to surround the concrete steel (6) and having a longitudinal slit (1a) at one side. The body portion (1) further comprises fixing tabs (4, 5) on the inside and gripping tabs (2, 3) on the outside for gripping the inner surface of the hole. The concrete steel (6) is inserted through the slit (1a) inside the body portion (1) so that the fixing tabs (4, 5) are positioned between the gripping protuberances (6a) of the concrete steel (6) and lock the anchoring means immovably in the longitudinal direction of the steel (6).

Description: Means for anchoring a rock bolt made of concrete steel in a drill hole The invention relates to an anchoring means for anchoring a rock bolt in a drill hole, comprising a body portion intended to be positioned around the rock bolt; gripping tabs projecting radially from the body portion, the tips of the gripping tabs being intended to be pressed against the inner surface of the drill hole; and a longitudinal slit extending over the entire length of the body portion; the body portion being arranged to yield resiliently on installing it around the rock bolt and comprising fixing tabs projecting from the body portion towards the inside of the body portion and being intended to be pressed against the outer surface of the rock bolt. Rock bolts are installed by grouting them in a drilled hole with resin or concrete, depending on the application. To install a bolt in a drill hole so that it stays in position during the grouting and especial¬ ly during the hardening of grout, various ways are used to anchor the bolt in the drill hole either at the end close to the rock surface or at the opposite end. One widely used anchoring arrangement comprises a wedge provided at the end of the rock bolt and an associated expansion part. When the bolt is inserted into the drill hole, the wedge penetrates inside the expansion part, thus spreading it against the surface of the hole while wedging the bolt in position. In this arrangement the bolt may be prestressed during the hardening of concrete to some extent by a nut attached to its one end so as to reinforce the rock. Another known way to anchor a rock bolt is to wedge it at the end close to the hole by means of separate wedges. In this case, the bolt cannot be prestressed, but the rock is reinforced merely by the bond formed between the bolt and the rock when the concrete hardens. DE 32 04 417 teaches an arrangement in which the bolt is anchored in the drill hole by means of a separate anchoring member placed around the bolt. The anchoring member is formed by a fixing sleeve having tooth-like projections at the edge. In this arrange- ment the sleeve is pushed over the bolt and the projections have been bent so that they touch the inner surface of the hole when the bolt is inserted into the hole. As the projections are directed towards the end close to the surface of the hole, they lock the bolt so that it cannot be easily withdrawn from the hole but will stay in position during the harden¬ ing of concrete. A drawback of this arrangement is that the projections are rather weak and the bolt cannot be prestressed before the drying of concrete but the projections merely keep the bolt itself in position. Moreover, the anchoring means of the DE document is not as such suitable for use when the bolts are concrete steels having a surface with protuberances to which the anchoring means cannot be attached. One object of the present invention is to provide an anchoring means for rock bolts which is suitable for use with various rock bolts and especial¬ ly with concrete steels and which is easy to install around such a rock bolt at a desired position. Another object of the invention is to provide an anchoring means by means of which the bolt can be prestressed reasonably immediately after it has been installed before the concrete has hardened. The anchoring means according to the invention is characterized in that the fixing tabs are inclined in opposite directions with respect to each other so that some fixing tabs prevent the sliding of the anchoring means in the longitudinal direction of the rock bolt against the insertion direction while the other fixing tabs prevent the sliding of the rock bolt in the opposite direction with respect to the anchoring means when the rock bolt is being prestressed, and that the width of the longitudinal slit of the body portion is such that the rock bolt can be inserted through the slit inside the body portion. An essential feature of the invention is that the anchoring means is made of a sheet-like portion bent into a curved shape such that it can be fitted around a rock bolt, thus forming a body portion with a longitudinal slit on one side in order that the body portion would yield resiliently when it is being installed around the rock bolt. An essential feature of the preferred embodiment of the invention is that the slit has a width such that the rock bolt, espe¬ cially a concrete steel used as a rock bolt, can be inserted inside the anchoring means. Another essential feature of the invention is that gripping tabs project from the body portion, the tabs having a greater width close to the body portion and tapering towards the tip and being bent so that the diameter of a circle drawn through the tips is greater than the diameter of a hole drilled for the bolt. Still another essential feature of the invention is that the body portion comprises fixing tabs projecting toward the inside so that the tabs will be positioned against the surface of the rock bolt, thus locking the anchoring means in the longitudinal direction of the rock bolt. Another essential feature of the preferred embodiment of the invention is that the body portion comprises gripping tabs at least at two points in its longitudinal direction. The preferred embodiment of the invention is further based on the idea that the body portion comprises fixing tabs projecting towards the inside of the body portion at least at two successive points in the longitudinal direction of the body portion. The preferred embodiment of the invention is further based on the idea that the anchoring means is made of a sheet in which the gripping tabs and the fixing tabs are formed either by cutting or by perforating the sheet in a suitable manner and then bending each tab in the respective direction. An advantage of the arrangement according to the invention is that the anchoring means is easy to install around the rock bolt by pushing it over the bolt from the end or preferably from the side, so that the anchoring means, being resilient, yields. In the preferred embodiment, the slit in the side of the anchoring means expands, thus allowing the rock bolt, such as a concrete steel, to pass through it. Another advantage of the anchoring means according to the invention is that the gripping tabs may be of a desired stiffness so that the rock bolt can be pre¬ stressed. Still another advantage of the anchoring means of the invention is that it is simple and easy to manufacture and the resulting operating costs are thus low. In the following the invention will be described in greater detail with reference to the attached drawings, in which Figure 1 is a schematic view of an anchoring means according to the invention as seen in the longitudinal direction of the rock bolt; Figure 2 is a schematic partial sectional side view of an anchoring means according to the invention when installed around a rock bolt; and Figure 3 is a schematic view of a blank for an anchoring means according to the invention before it has been bent into a desired shape. Figure 1 shows an anchoring means according to the invention, comprising a body portion 1 and gripping tabs 2 and 3 projecting outward from the body portion. The anchoring means further comprises fixing tabs 4,5 projecting towards the inside of the curved body portion 1 (only the upper fixing tabs are shown in the figure). The body portion 1 is curved in such a way that it surrounds a rock bolt 6, such as a con¬ crete steel used as a rock bolt, partially when installed in position. The body portion 1 has on one side a slit la having a width smaller than the dia¬ meter of the rock bolt at the installation point of the anchoring means. Moreover, the body portion 1 is arranged to yield so that a rock bolt, such as a concrete steel, can be inserted through the slit la inside the body portion 1 of the anchoring means. The gripping tabs 2 and 3 are relatively wide at the end close to the body portion 1 and taper towards the tip so that the tip portions will be suitably flexible while they, however, are very firm and rigid, resist- ing even a relatively high load when installed in the drill hole. Furthermore, the shape of the gripping tabs enables the bolt with its anchoring means to be inserted into a hole filled with concrete as the relatively wide gaps between the gripping tabs allow a free flow of the concrete. In the preferred embodiment the gripping tabs 2 and 3 are unequal in length. This is because the diameter of the drill bit decreases as the drill bit wears out. The inner diameter of the formed hole thereby decreases correspondingly, and the longer gripping tabs 2 may be bent excessively in parallel with the walls of the hole so that their ability to lock the bolt in position deteriorates. As the shorter gripping tabs 3 thus remain at a wider angle, they ensure that the bolt will be anchored reliably even when using drill bits worn out in different ways. The gripping tabs 2 and 3 of the anchoring means also centre the upper end of the bolt in the hole, thus ensuring that the concrete or resin used as a grouting material will surround the bolt on all sides. This is especially important in order that the bolt could be separated from ground water causing the bolt to be corroded. When the concrete or resin surrounds the bolt on all sides over its entire length, cor- rosion can be prevented and thus the bolt will not deteriorate and possibly break in the long run. If the bolt is to be centred reliably over its entire length, it can be provided with a number of anchoring means with suitable mutual spacings in the axial direction of the bolt. Figure 2 is a partial sectional side view of the anchoring means according to the invention when installed around a rock bolt. As appears from the figure, the upper fixing tab 4 and the lower fixing tab 5 are positioned between gripping protuberances 6a on the surface of a concrete steel used as the rock bolt and lock the anchoring means longitudinally immovably around the concrete steel. The gripping tabs 2 and 3 project obliquely outward from the body portion 1 so that the concrete steel with its anchor¬ ing means can be pushed into a rock hole. As the outer dimension of the bolt with the anchoring means is larger than the diameter of the hole, the tabs 2 and 3 bend, remaining in an inclined position with respect to the inner surface of the hole. After the rock bolt 6 has been pushed to the bottom of the drill hole, it has been locked in position in the hole, and the tabs 2 and 3 press the body portion 1 against the concrete steel, thus keeping the fixing tab between the pro- tuberances 6a of the concrete steel so that the concrete steel cannot be detached from the anchoring means. Figure 3 shows a blank for the preferred embodi¬ ment of the anchoring means according to the inven- tion. The blank has been cut out of a metal sheet. At the same time the edges of the fixing tabs 4 and 5 and the gripping tabs 2 and 3 have been cut so that they can be bent outward from the sheet. The anchoring means is obtained from the blank by bending the fixing tabs 4 and 5 in one direction and the gripping tabs 2 and 3 in the opposite direction with respect to the body portion 1 and bending the body portion 1 into a curved shape, as shown in Figure 1. The anchoring means according to the invention is simple and inexpensive to manufacture and extremely easy to use. The anchoring means is installed around a rock bolt, such as a concrete steel, simply by pushing it in position in the transverse direction of the rock bolt, so that, being made of steel of a suitable thickness, the body portion 1 yields, allowing the slit la to enlarge so as to correspond to the outer dimension of the rock bolt. The gripping tabs 2 and 3 and the fixing tabs 4 and 5, being similarly made of a material of a suitable thickness, anchor the rock bolt, such as a concrete steel, so firmly to the inner surface of the hole that the bolt can be prestressed for reinforcing the rock before the grout, such as concrete, has hardened. The invention has been described above and in the drawings by way of example, and it is not re- stricted to the embodiment disclosed. The anchoring means need not be made as described above, i.e. by cutting and bending a sheet, but it may also be made by casting or in some other suitable manner, provided that the structure and operation are essentially similar. The number of the gripping tabs need not be three, as in the figures, but it may vary, if only the tabs are sufficiently rigid and firm. The gripping tabs may be positioned at a single point in the longitudinal direction of the bolt or more than two successive tabs may be provided. The body portion 1 need not necessarily be bent into a uniformly curved shape but it may also be gently angular in shape or of any other suitable shape, provided that it surrounds the concrete steel essentially on all sides, as shown in the figures, and that its fixing tabs are posi¬ tioned between the protuberances 6b of the surface of the concrete steel. The fixing means may be advan¬ tageously and easily made of steel or steel sheet but other materials of sufficient strength, such as various metals and alloys, are possible as well. The anchoring means according to the invention may be used not only with a concrete steel described by way of example but also with rock bolts of other kinds, such as smooth rock bolts, rock bolts having protuberances or recesses on the surface, etc. With a smooth rock bolt, it is preferable that the tips of the fixing tabs are sharp so that they penetrate into the smooth surface of the bolt, thus locking the anchoring means to it. With rock bolts having a surface with pro¬ tuberances or recesses, it is not essential that the tips are sharp but the tips of the fixing tabs may be blunt or even curved in shape. When the fixing tabs are suitably shaped, the rock bolt may be installed in the anchoring means from the end of it, and the longitudinal slit enables the inner diameter of the anchoring means to be enlarged when the rock bolt is pushed inside it from the end. In the preferred embodiment, the longitudinal slit of the anchoring means, however, is so wide that the rock bolt can be inserted from the side of the anchoring means so that the anchoring means is simpler and easier to install along the length of the rock bolt.

Claims: Claims : 1. Anchoring means for anchoring a rock bolt (6) in a drill hole, comprising a body portion (1) intend- ed to be positioned around the rock bolt (6); gripping tabs (2, 3) projecting radially from the body portion (1), the tips of the gripping tabs being intended to be pressed against the inner surface of the drill hole; and a longitudinal slit (la) extending over the entire length of the body portion (1); the body portion being arranged to yield resiliently on installing it around the rock bolt (6) and comprising fixing tabs (4, 5) projecting from the body portion (1) towards the inside of the body portion and being intended to be pressed against the outer surface of the rock bolt (6), c h a r a c t e r i z e d in that the fixing tabs (4, 5) are inclined in opposite directions with respect to each other so that some fixing tabs (5) prevent the sliding of the anchoring means in the longitudinal direction of the rock bolt (6) against the bolt feeding direction while the other fixing tabs (4) prevent the sliding of the rock bolt (6) with respect to the anchoring means in the opposite direction when the rock bolt is being prestressed, and that the width of the longitudinal slit (la) of the body portion (1) is such that the rock bolt (6) can be inserted through the slit (la) inside the body portion (1). 2. Anchoring means according to claim 1, c h a r a c t e r i z e d in that at least three fixing tabs (4, 5) are provided substantially at the same point in the longitudinal direction of the body portion (1) on different sides of the body portion, and that fixing tabs (4, 5) are provided at least at two mutually spaced points in the longitudinal direction of the body portion (1). 3. Anchoring means according to claim 1 or 2, c h a r a c t e r i z e d in that there are at least three gripping tabs (2, 3) around the body portion (1) on its different sides. 4. Anchoring means according to claim 3, c h a r a c t e r i z e d in that there are gripping tabs (2, 3) at least at two mutually spaced points in the longitudinal direction of the body portion (1). 5. Anchoring means according to claim 3 or 4, c h a r a c t e r i z e d in that the width of the gripping tabs (2, 3) is at its greatest at the end close to the body portion (1), and that the gripping tabs taper towards their tips to be positioned against the surface of the drill hole. 6. Anchoring means according to any of claims 3 to 5, c h a r a c t e r i z e d in that it comprises gripping tabs (2, 3) of at least two different lengths, the gripping tabs (2, 3) positioned at the same point in the longitudinal direction of the anchoring means being equal in length. 7. Anchoring means according to any of the preceding claims, c h a r a c t e r i z e d in that it is made of a sheet by cutting so that one edge of the fixing tabs (4, 5) and the gripping tabs (2, 3), respectively, adjoins the sheet, and bending the blank so obtained into the body portion (1) having the fixing tabs (4, 5) bent towards the inside of the body portion (1) and the gripping tabs (2, 3) bent outward from the body portion at a desired angle. 8. Anchoring means according to any of the preceding claims, c h a r a c t e r i z e d in that the fixing tabs (4, 5) are sharp at the end to be positioned against the rock bolt (6) so as to enable them to grip the substantially smooth surface of the rock bolt (6).

Inventors: LAUNIEMI MARKKU, LAUNIEMI, MARKKU
Applicants: LAUNIEMI MARKKU, TAMROCK OY, LAUNIEMI, MARKKU
Application year: 1994
Main classification: E21D21
IPC codes: E21D20, E21D21